1. Field of the Invention
The present invention relates to viewing ports for contaminated environments, and more particularly to a dirt shield for a viewing port which prevents contaminants or particulates from adhering to the viewing window of the port.
2. Description of the Prior Art
There are many applications for the use of a viewing port with respect to contaminated or hostile environments for the purpose of taking measurements or observing the internal conditions or change of the environment. Examples of such situations include smoke stacks, steel producing retorts, and chemical reaction vessels. In many applications, in addition to viewing internal conditions, measurements are made across the contaminated space by using transmitted light or radiation. It is the purpose of the viewing port to isolate from the contaminated environment the instruments or persons which take the measurements or make the observations.
The present industrial technique for maintaining a clean instrument optical lens, or viewing windows of a port, involves simply the use of a purging gas inletted around the window of the port. If the contamination is light, such techniques may be effective. However, for environments which have a high soot or ash content, as is associated with the combustion of coal in a fossil-fired commercial power or steam generation plant, the technique is insufficient. It is necessary to schedule frequent manual cleanings of the view port windows. Such cleanings can cause disruption of the instrument operation or possibly cause damage to the window itself. In addition, such cleanings are costly and render the instruments ineffective during the period of time that it takes for the cleaning operation to be completed.
The present invention provides a dirt shield for viewing ports which includes the formation of a cone of flow of gas disposed in front of the window of the port combined with a flow of ionized gas between the window and the cone of gas.